The use of elongated flexible guidewires for help in positioning both diagnostic and therapeutic catheters within a patient is well known in the prior art. In accordance with such a procedure, an elongated guidewire having a flexible tip at one end is inserted within the patient's cardiovascular system and routed into the patient. Progress of such a guidewire is monitored by an attending physician on a viewing screen. To facilitate viewing of the distal end of the guidewire as it progresses through the patient, it is known in the prior art to utilize an x-ray opaque material for the guidewire tip. Once the guidewire has been positioned within the patient, the elongated catheter is slipped over the guidewire and routed to a desired position within the patient.
Two examples of prior art guidewires are disclosed in U.S. Pat. Nos. 3,906,938 to Fleischhacker and 4,545,390 to Leary. Each of these prior art patents discloses a guidewire having a flexible spring at the guidewire's distal end. Beneath the spring is a core wire tapered to a reduced diameter. The combination of the tapered core wire and the flexible spring provides a distal tip which can be bent into a desired configuration by the attending physician prior to guidewire insertion and in addition, provides a flexible enough tip so that when interior blood vessel walls are encountered as the guidewire is inserted, the tip will bend without puncturing the blood vessel walls.
In fabricating a multi-piece guidewire, core wire is fabricated and the flexible spring then attached to the distal end of the core wire using a welding or soldering technique known in the art. Prior art fabrication techniques for the core wire involve centerless grinding of the core wire to produce a tapered transition region and reduced diameter distal end. In addition, the prior art suggests flattening the tapered end portion to increase even further flexibility of the core wire.
The prior art practice of centerless grinding the core wire to reduced diameter portion has certain limitations. During fabrication of the core wire, a drawing process is used to achieve an initial core wire diameter. During this drawing process, the outside surface of the core is work hardened. During the grinding process that tapers the core wire, the outside skin of the wire is removed and the tapered portion is softer than the larger diameter portion of the guidewire.
The prior art centerless grinding technique is difficult to perform over long lengths of small diameter wire. This is due to the fact that the small diameter wire tends to break during the grinding process. In addition, known technology cannot produce diameters small enough for certain uses wherein the guidewire must be inserted into small blood vessels.